Conventionally, a photosensitive film having a photosensitive layer formed by coating and drying a photosensitive composition on a support, has been used for forming a permanent pattern with a material, such as a solder resist. As a method of forming a permanent pattern with a material, such as a solder resist, hitherto, there is a method of forming a laminate by: laminating a photosensitive film on a substrate, such as a copper clad laminate, on which a permanent pattern is formed; exposing the photosensitive layer of the laminate; forming a pattern by developing the photosensitive layer after exposing it; and performing a hardening treatment, and the like.
For a photosensitive composition using a polyurethane resin as a binder for the solder resist, improving bending resistance and flame retardancy is an important task to be achieved, and various studies have been made in this regard.
For example, a photosensitive composition containing (A) an acid-modified and vinyl group-containing novolac type epoxy resin having a biphenyl skeleton, (B) a polyurethane resin, (C) a phosphorus-containing compound, (D) a photopolymerizable compound (D) having at least one ethylenically unsaturated group in the molecule, and (E) a photopolymerization initiator, in which (B) the polyurethane resin is a reaction product of an epoxy acrylate compound having an ethylenically unsaturated group and two or more hydroxyl groups, a diisocyanate compound, and a diol compound having a carboxyl group, is proposed. (see, for example, JP-A-2009-251585 (“JP-A” means unexamined published Japanese patent application)).
In addition, a photosensitive composition for a rigid printed wiring board containing a carboxyl group-containing photosensitive urethane resin (A), a photopolymerization initiator (B), an ethylenically unsaturated group-containing photosensitive compound (C), and a thermal hardening compound (D), in which the carboxyl group-containing photosensitive urethane resin (A) is a resin prepared by reacting a carboxyl group in a carboxyl group-containing urethane prepolymer (a) obtained by reacting a polymer polyol (e), a carboxylic acid compound (f) having two hydroxyl groups in the molecule, and a diisocyanate compound (g) as essential components, with an epoxy group or an oxetane group of a compound (b) having an epoxy group or an oxetane group and an ethylenically unsaturated group, and reacting a hydroxyl group in the resultant hydroxyl group-containing urethane prepolymer (c) with an acid anhydride group of an acid anhydride group-containing compound (d), is proposed (see, JP-A-2009-271290). In the examples of the publication of JP-A-2009-271290, a polyurethane resin added with a phosphazene compound or polyphosphoric acid melamine salt is described. Further, a photosensitive flame retardant resin composition in which the same urethane resin as the carboxyl group-containing photosensitive urethane resin described in JP-A-2009-271290 is combined with a specific amount of phosphinic acid salt having a specific volume average particle diameter is proposed (see, JP-A-2010-117452).
As described above, although it is required for a photosensitive composition used for a flexible printed circuit (FPC) to have excellent flame retardancy as well as excellent bending resistance, the flame retardancy and bending resistance are in the relationship of trade-off. Thus, there has not been developed yet a photosensitive composition having both of excellent flame retardancy and excellent bending resistance, and further having excellent resolution, excellent insulation reliability, and reduced warp (or bow), a photosensitive film and a photosensitive laminate, a method of forming a permanent pattern, and a printed board using the photosensitive composition.